1. Field of the Invention
This invention relates to a method and apparatus for producing biofuels. In one aspect, this invention relates to a method and apparatus for producing biofuels from bio-oil, for example, animal fat. In one aspect, this invention relates to an electrochemical method and apparatus for producing biofuels. In one aspect, this invention relates to a photo electrochemical method and apparatus for producing biofuels.
2. Description of Related Art
Bio-oil is a biomass-derived synthetic liquid fuel used as a substitute for petroleum which is typically produced by pyrolysis of biomass. Bio-oil includes bio-crude, which contains high oxygen content, water, and carboxylic groups. By way of example, bio-crude could be vegetable oil, animal fat, and the like.
Biofuel is a solid, liquid, or gaseous fuel obtained from relatively recently lifeless or living biological material and is different from fossil fuels, which are derived from long dead biological materials. Biofuel is a clean form of bio-oil and is suitable for direct use.
Photoelectrochemistry is the study of the interaction of light (in particular, radiation in the “sunlight” region, about 87 to 308 kJ/mole or about 0.9 to about 3.2 eV per photon) with electronic flow and chemical reactions at the electrode surfaces in electrochemical cells. The radiation involved in this process has considerable energy and can be used for the direct production of electricity, the splitting of water into hydrogen and oxygen, referred to as photoelectrolysis, and the treatment of organic species. However, to be practical, efficient and inexpensive systems utilizing readily available materials must be devised for the conversion process. The hindrances to practical applications of the system include the poor stability and low efficiency of the photoelectrode due to photoelectrochemical reactions involving photon-electron transfer and recombination, redox exchange and surface corrosion.
Numerous efforts have been made to enhance the efficiency and stability of photoelectrochemical cells. The general approach has been to coat a layer of protective materials, which may be organic substances, active metal ions, noble metals, light sensitive dyes and more stable semiconductors, such as metal oxides, onto the photoelectrode surface. Recent developments include a thin film dye to sensitize the semiconductor electrodes in photoelectrochemical cells.
U.S. Pat. No. 7,037,414 teaches a photoelectrochemical cell comprising a light transmissive enclosure, two photoelectrodes, a semiconductor photoanode and a semiconductor photocathode, disposed within the light transmissive enclosure, and an electrolytic solution disposed entirely between the photoelectrodes. Because the electrolytic solution employed in the photoelectrochemical cell is limited to a volume disposed between the photoelectrodes, the sunlight is able to directly shine on the catalyst surfaces of the photoelectrodes to produce hydrogen and oxygen, thereby eliminating solar energy losses due to water (electrolyte) sorption; and because there is no thick water (electrolyte) layer between the sunlight and the catalyst surfaces, the product gases, hydrogen and/or oxygen, are able to leave the catalyst surface easily without any restriction imposed by water surface tension. That is, the three-phase (gas, solid catalyst and liquid electrolyte) area is optimized to increase the solar energy efficiency. The photoelectrodes comprise photo electro-catalysts are bound together by a polymer electrolyte, such as NAFION, a perfluorosulfonic acid polymer available from DuPont, to form a catalyst layer. The polymer electrolyte performs a multitude of functions including gas separation, water containment, proton exchanger and water transporter. The ionomer of the polymer electrolyte in the catalyst layer acts as a capillary channel to transport water to the catalyst surface and as an electron conductor to transport electrons between the two photoelectrodes. In addition, this fully hydrophilic ionomer helps to distribute water to the catalyst surface without blocking the incoming solar energy.
More than 70 different catalytic reactions (oxidations, hydrogenations, dehydrogenations, isomerizations, decompositions) have been electrochemically promoted on Pt, Pd, Rh, Ag, Au, Ni, IrO2, and RuO2 catalysts. The solid electrolytes are O2− conductors, such as Y2O3 stabilized ZrO2 (YSZ), H+ conductors, such as CaZr0.9In0.1O3-α and NAFION®, F− conductor (CaF2), and the like. Deoxygenation and decarboxylation are rarely reported at high temperatures with big molecules, for example, chains with more than five carbons. However, in the liquid phase, decarboxylation has been reported. See, for example, U.S. Pat. No. 6,238,543, which teaches a process for electrolytic coupling of carboxylic acids carried out in a polymer electrolyte membrane reactor in which gaseous or neat (i.e. without water) liquid reactants are used without the use of organic co-solvents while preventing the loss of platinum and permitting the use of oxygen reduction to water as the cathode reaction. In this case, the use of a neat organic acid is necessary to prevent oxygen production at the anode electrode. Consequently, the method disclosed therein, which is necessarily carried out at temperatures less than 120° C. due, among other things, to limitations of the NAFION electrolyte employed therein and which requires cell potentials of at least about 3.0 volts, cannot be used for bio-oil treatment due to the presence of about 17% by weight water therein.